Nausea, gas, cramping, stomach pain, and diarrhea during or after training is unfortunately common in athletes. Vigorous or high intensity exercise in particular may trigger gastrointestinal (G.I.) symptoms, and endurance athletes are especially prone to G.I. issues. While these symptoms are temporary, they’re certainly not fun or helpful for performance!
There are many potential causes of G.I. issues during training, including changes in blood supply to the digestive system, changes to motility, hydration status, the impact of the activity, and even the posture of the athlete. For example, runners may experience more diarrhea because of the impact of running, while cyclists may experience more upper G.I. pain due to posture .
Nutrition certainly plays a role in G.I. issues during training and is perhaps the most important factor to address because of the amount of control athletes have over it given a bit of forethought. Here are some tips to help you fuel comfortably!
Support stomach emptying with meal composition and timing
While consuming fiber, fat, and protein is important in everyday life to promote stable blood sugar levels, they can create G.I. issues for athletes as each of these dietary factors slow gastric (stomach) emptying. This is especially important for high-intensity exercise, while low intensity exercise is often more tolerable.
As a rule of thumb, athletes should change the macronutrient balance of their meals as they get closer to training by transitioning to more carbohydrates while limiting fiber, fat, and protein. In the hour before training, it is usually best to consume only carbohydrates, especially in preparation for high-intensity training. For large, mixed meals, it’s a good idea to place these three hours prior to exercise unless the athlete knows they tolerate otherwise!
However, pre-training fuel is highly individual and also depends on the specific training. Fiber, fat, and protein can certainly be consumed before exercise as comfort permits to increase satiety, promote recovery, and meet energy needs.
For individuals sensitive to fiber before training, they may want to consider paying attention to high FODMAP foods, which contain short-chain carbohydrates that are poorly absorbed, osmotically active, and highly fermentable, leading to a number of G.I. symptoms. While high FODMAP foods, such as onion, garlic, broccoli, apples, pears, avocados, and lentils, are beneficial for gut health and should be generally tolerated on a day-to-day basis, some individuals are more sensitive and benefit from avoiding them before and during training .
It should be stressed that high FODMAP foods should never be completely restricted in everyday life as they’re highly beneficial for the microflora in the large intestine. If an athlete finds they need to restrict FODMAPs daily in order to ease digestive issues, they should seek professional help.
Be specific about the carbohydrate concentration of sports drinks
Sports drinks with a high carbohydrate concentration can cause G.I. issues due to the accumulation of carbohydrates in the small intestine and water retention. It’s recommended to choose beverages with a concentration of 5-8% carbohydrate . Choosing a carbohydrate powder that you mix on your own, such as Gnarly Fuel2O, allows you to personalize the carbohydrate percent to a level that is tolerable to you, especially as some athletes prefer a much lower percentage of carbohydrates.
Additionally, the type of carbohydrate consumed during exercise can impact G.I. issues. For intakes under 60g of carbohydrates per hour, the type of carbohydrate can be single or multiple (e.g. only glucose). However, for those participating in endurance events who may need upwards of 90g of carbohydrates per hour, it’s essential to mix the carbohydrate type (e.g. glucose and fructose) to aid absorption in the small intestine and reduce G.I. discomfort. Entirely fructose beverages should be avoided .
Keep in mind that consuming gels does not negate the need for water! Gels have a high carbohydrate content and are intended to be taken with plenty of water to aid absorption and reduce G.I. discomfort.
Dehydration can exacerbate G.I. issues during training and is an easy solution to many G.I. issues. Therefore, athletes should always begin training in a hydrated state, and the best way to check your hydration status is to take a look at your urine stream - it should be pale yellow! As a rule of thumb, drink 7-12oz 30 minutes prior to training and 4-8oz every 15-20 minutes .
Nourish your gut daily
Supporting digestive health every day promotes regular bowel movements, which translates to increased comfort and decreased gas and bloating for athletes. Additionally, the gut is essential for allowing us to use nutrients from food, and the microbiome plays an important role in mitigating inflammation and promoting recovery. To nourish the gut daily, it’s important to eat a diet with plenty of fiber from a diverse range of fruits, vegetables, nuts, and seeds. Fermented foods such as kimchi, sauerkraut, and kefir are also beneficial food sources of probiotics to promote a diverse microbiome.
Finally, NSAIDs are commonly used by athletes to relieve pain or even used in anticipation of pain, but their prolonged and regular use can compromise the mucosal lining of the gut and may contribute to increased G.I. complaints during exercise .
Be aware of RED-S and digestive issues
Relative Energy Deficiency in Sport (RED-S) occurs when insufficient calories are consumed to support the energy expenditure of exercise. RED-S occurs in both males and females and compromises physiological processes, including digestion . Some symptoms associated with this include constipation, gas, bloating, acid reflux, and undigested food in the stool. If altering what you eat before and during exercise does not alleviate your digestive issues, or if your digestive issues occur outside of training, you may want to consider digestive disorders and your overall energy intake.
Don’t forget to experiment with fueling strategies
As a final note, it’s great to experiment with different fueling strategies so that you know what works for you and what doesn’t. However, experiment only when it’s okay if you end up experiencing G.I. issues. In other words, don’t experiment with a new nutrition strategy on race days or if you’re going to be stuck outside for the rest of the day with miserable G.I. issues!
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Killian, L. A., Muir, J. G., Barrett, J. S., Burd, N. A., & Lee, S. Y. (2021). High Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols (FODMAP) Consumption Among Endurance Athletes and Relationship to Gastrointestinal Symptoms. Frontiers in nutrition, 8, 637160. https://doi.org/10.3389/fnut.2021.637160
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